1. Field of the Invention
The present invention relates to a lip type seal made of a resin such as PTFE and the like for use in high pressure fuel pump such as an injection pump employed in a gasoline direct injection engine, and for use in other general hydraulic or pneumatic pressure equipments.
2. Description of the Conventional Art
The use environment of the two fluid sealing which used in a plunger of an injection pump for sealing the gasoline and engine oil tends to become increasingly severe in consequence of superior performance of the injection pump for the gasoline direct-injection engine. It is required for the sealing device to improve resistance to pressure and chemical resistance as a countermeasure against bad fuel, and to this end, it has been proposed in these days that the conventional oil seal is changed to a lip type seal made of resin such as PTFE.
A conventional lip type seal 101, as shown in FIG. 7, has inner and outer circumferential lips 103 and 104 which have an approximately cylindrical recessed portion 102 opening toward a first sealing fluid side A, provided at inner and outer peripheries of the cylindrical recessed portion 102, and are slidably in contact with a shaft and a housing respectively, and a plate-like lip 105 which has an approximately wedge-shaped recessed portion 106 opening toward the shaft at a second sealing fluid side B and is provided at the second sealing fluid side B of the wedge-shaped recessed portion 106, where the inner and outer circumferential lips 103 and 104 are formed integrally with the plate-like lip 105 into one-piece structure made of resin. When the shaft 107 is inserted toward the inner periphery side in a direction indicated by a big arrow X, the plate-like lip 105 is bent largely around a tip point A of the approximately wedge-shaped recessed portion 106 in a direction indicated by an arrow Y, and an interference is secured by its reactional restoration force. However, since the lip type seal 101 is made of resin, it has a disadvantage of lowered sealability due to reduced interference of the plate-like lip 105 caused by poor creep characteristics of the resin. That is to say, since the sealing is effected by the reactional restoration force of the plate-like lip 105 bent around the tip point A, there would be a potential rupture due to stress concentration onto the tip point A, and besides rupture, there is a disadvantage of reduced interference of the plate-like lip 105 due to creep.
Further, comparing with one made of a rubber material or the like, the resin-made lip type seal has disadvantages of poor resilient characteristics, reduced adhesion to the shaft, and reduced sealability.
Incidentally, Japanese unexamined utility model publication No. 61-117962 and Japanese unexamined patent publication No. 2000-320689 disclose an oil seal attached to the retaining ring wherein serrated patterns are formed on the lip, however, nothing is disclosed about a lip type seal made of resin.